The present invention relates to the field of pressure transducers, and in particular to the field of pressure transducers that include a temperature compensated pressure transmitter and a pressure sensor.
Typically, pressure-measuring devices consist of a pressure transmitter and a pressure sensor coupled with the pressure transmitter. The pressure transmitter is subjected externally to a pressure, which is coupled to and measured by the pressure sensor. The pressure transmitter often serves to protect the extremely sensitive pressure sensor. The pressure transmitter includes a separating membrane that seals off the pressure transmitter, and which together with a base body of the pressure transmitter defines a chamber that contains a pressure-transmitting medium. The materials of the base body and the separating membrane that together form the chamber typically have significantly lower coefficients of thermal expansion than the pressure-transmitting medium. Because of this difference, temperature changes in the environment lead to differing expansions in the base body, the separating membrane, and the pressure-transmitting medium. This often results in relatively large measurement errors.
To reduce these temperature-induced measurement errors, pressure transmitters have been designed that have a separating membrane with a comparatively large surface area on the process side. Alternatively or additionally, the volume of the pressure-transmitting medium in the chamber is reduced. However, the volume of the pressure-transmitting medium cannot be reduced at will because of the desired measuring range of the pressure sensor or its measurement tolerances. Moreover, a pressure transmitter with a very small separating membrane diameter is often required, since space considerations alone often place limits on the size of the separating membrane in terms of area.
GM 76 03 126 describes a pressure transmitter in which an equalizing part with a minimal expansion coefficient is built into the chamber of the base body of the pressure transmitter to compensate for the volume expansion of the pressure-transmitting medium. However, such a pressure transmitter is extremely difficult to produce. In addition, adjusting this temperature-compensated pressure transmitter to provide exact setting of the proportions of the pressure-transmitting medium and the equalizing body is extremely expensive. Finally, particularly with pressure gauges for measuring pressures in the millibar range, it is necessary for the pressure transmitter to transmit the pressure received from the outside reliably and evenly to the pressure sensor downstream thereof. However, with the pressure transmitter described in GM 76 03 126, in which the equalizing part floats freely in the chamber, this is not possible or is possible only to a limited extent.
Therefore, there is a need for a temperature compensated pressure transmitter for use in a pressure transducer.